Cold cathode abnormal glow gas discharge created electron beams have been used for pumping gas lasers, processing microelectronic films, and for soft vacuum lithography. The cold cathode can be constructed of a variety of materials, including metals such as aluminum, magnesium, molybdenum or stainless steel, metal-ceramic composites such as Si-SiO.sub.2, Al-Al.sub.2 O.sub.3, Mo-Al.sub.2 O.sub.3, Mo-MgO, or metals with thin insulating or semi-insulating surface layers such as aluminum with an Al.sub.2 O.sub.3 surface layer or silicon with an SiO.sub.2 surface layer. Generally, the secondary electron emission coefficient, v, of the cathode material following ion and photon bombardment determines the cold cathode electron beam generation efficiency via the v/(1+v) factor. Typically, metals have v&lt;1 and ceramic composites have v&gt;1. The cathode front surface exposed to the abnormal glow discharge may be of a variety of geometric shapes to electrostatically shape the electron beam emitted. Large area beam sources, focused line source beams, and spot beam sources are but three illustrative examples.
In the prior art relating to glow discharge created electron beams electron emission was purposely restricted to the cathode front face by employing a separate cathode shield to prevent electron emission from other cathode surfaces. Cathode shielding was necessary because the entire cathode was immersed in the abnormal glow discharge region located inside the vacuum chamber. In the absence of a shield the entire cathode is exposed to the abnormal glow gas discharge, resulting in electron emission from all exposed cold cathode surfaces. In this prior art shielded cathode configuration, water cooling of the cold cathode located inside the vacuum chamber always required complex mechanical and vacuum construction. For example, the size of the mechanical spacer between the cathode shield and the cold cathode itself is typically a fraction of a millimeter in thickness and must be of precise geometric construction. The typical tolerance is .+-.0.1 millimeter along the entire length of the cold cathode-to-cathode shield periphery. For high power operation of the cold cathode an internal cooling system must be included for exhausting heat created by ion bombardment of the cold cathode. Degradation of the cathode front face occurs due to ion bombardment erosion. For this reason, frequent cathode replacement or cathode front face cleaning must also be carried out in order to maintain the stability and uniformity of the abnormal glow discharge created electron beam.
In summary, the prior art cold cathode configurations which attempt to satisfy both electrical cathode shielding and internal thermal cooling are complex in mechanical design and construction, are costly, and exhibit low reliability.